It's not. It's a tiddler. Sure, it may be the biggest building in Western Europe – at least until Paris's Hermitage Towers are finished around 2015 – but compared to really tall buildings, it hasn't got a chance.

Via the Mirror, here's a view from the top of the building:

For the sake of comparison, here's that same view replicated using Google Earth, with all those pretty 3D buildings:

Here's what it looks like if you put the Burj Khalifa, the biggest building in the world, at the same location:

The Gherkin is dwarfed in the bottom right, and see that green line in the middle distance? That's Hertfordshire. This is what tall looks like.